Measuring device



June 30, 1925. 1,544,090

0. EPPENSTEIN MEASURING DEVICE Filed June 19. 1923 Patented June 30, 1925.

UNITED STATES PA OTTO EPPENSTEIN, F JE'NA, GER-MANY, ASSIGNOR TO THE FIRM 0F CARL ZEISS, OF

JENA, GERMANY. 1

MEASURING DEVICE.

Application filed June 19, Serial No. 846,882.

' To ail whom it may concern. a

possible accuracy, it has proved suitable to dispose in these devices, according to a principle laid down by Ernst Abbe, the two distances to be compared in a straight line, i. e. in succession because in that case the result of the measurement is almost not affected by faulty deviations ofthe guides in which the parts to be displaced for carrying out the comparison, e. g. the two distances themselves are disposed. However, this arrangement has the drawback that the measuring device becomes comparatively long, viz, at least equal to double the length of the object to be measured, so that the aforesaid Abbe principle can, as a rule, only be applied in devices for shorter objects.

According to the present invention it is possible to attain the same accuracy of'the measurement as hitherto by providmg in a device, in which the two distances to be compared are disposed side by side, for sighting atone of the two distances a fixed sighting device in front of whiclktthere is disposed an optical system, displacea le parallelly to the distances of which system firstly the o tical axis lies 1n the plane determined by the two distances, of which secondly the front focal point lies on the distance to be-sighted at bythis system and of which thirdly that point lies on the other of the two distances which has the property that a ray aiming at it in the object-space emanates from the optical system at an angle to the axis which is equal to that on entering with respectto magnitude and sign.

The sighting device, which. is suitably constructed as a telescope provided with a sighting mark, replaces in conjunction with the optical system disposed in front a displaceable microscope as hithcrtousedfor sighting at a distance in the devices of the present kind. It can easily be provedthat with the arrangement according to the invention of the displaceable, optical system, also with the distances lying side by side, the errors of the measurement arising through faulty deviations of the guides kee within the samelimits as in the event 0 adhering to the aforesaid Abbe principle, by taking into accountthat also with rotations of the optical system, located in front of the sighting device, about the above described point the direction of the pencil of parallel rays emerging from the system is preserved, and

that a rotation about any axis perpendicular to the plane containing the two distances can be re laced by a rotat1on about an axis pass- 1n t roughthls point of the movable optica system and being also perpendicular to the said plane. v

Of. course, the optical system located in front of the sighting device must be so constructed that even with a displacement the ray pencil emerging from it always gets into the sighting'de'vice. In order to attain this result, the system must contain besides a number of lenses a number of reflecting surfaces by which the ray pencil is deflected in the requisite way. If the number of reflectin surfaces present be even, the aforesaid point of the system is formed by the front positive nodal point of the lens arrangement.

f, however, the number of reflecting sur-- faces be odd, it is the front negative nodal point of the lens arran ement which, owing to the inversion of the image effected in this case by the mirrors, forms the aforesaid point of the whole displaceable system. The

plane and by. a displacement in this use of an odd number of reflecting surfaces may, for instance, prove necessary if a lens arrangement be chosen, whose front positive nodal point is not accessible, e. g. because it lies within a lens.

Fig. 1 of the annexed drawing diagrammatically shows a device for comparing two scales. 2 is a side elevation of a constructural example and Fig. 3 a plan elevation thereof.

The. scales of the device shown in Fig. 1 are denoted by a and b. The first-named scale is sighted at b means of a nficroscope 0 which is dispose perpendicularly to the drawing plane. For sighting at the scale 6,

whose single divisions are actually directed perpendicularly to the drawing plane, serves a fixed sighting telescope consisting of an objective d and an ocular e, in front of which telescope in the telescope there is disposed an optical system consisting of a dispersive lens f, a lens 9 and a pentagonal prism 72;. The optical axis of this system lies just as that of the lane determined by the scales a and I). he microscope c and the optical system f, g, h are rigidly connected and jointly displaceable in a guide parallelly to the scales a and I). The front focal point of the lens system f, g, denoted by F, lies on the scale 1), so that the pencil of rays imaging the scale I) and emanating from the prism It and entering the telescope ll, c consists of parallel rays. The front positive nodal point of the system 7, g, denoted by K, lies on the scale a.

If it be desired to compare the scales 0' .and b, it is necessary to adjust successively,

the system f, g, h and the microscope 0, either the microscope 0 or the system 1, g, h to difi'erent divisions of the respective scale and'to read off in the other displaceable part the position of the corres onding divisions of the other scale relatively to the respective sighting mark. As

by displacing the guide in which the microscope c and thev system 7, g, h are displaceable is generally not exactly straight-lined, the microscope c and the s stem 1, g, it generally experience with a isplacement an additional rotation. However, it is obvious that with the arrangement chosen a slight rotation of the displaceable parts about an axis parallel to the scales a and b and about an axis containing the focal point F and the nodal point K as well as about an axis passing through the nodal point K and being perpendicular to the drawing plane and therefore also about an axis running in an optional direction only causes reading errors of the second order and is consequently harmless.

In the device shown in Figs. 2 and 3 there is fixed upon a base plate '5 a gripping appliance for a screw spindle}, consisting of two bearing pedestals k and 70 provided with points j and 7' In addition, the base plate z carries a sighting telescope m having a broken axis, a guide bar n and upon a su port 0 a measure p with a scale 72. On t e spindle Z, of which the whole length or a part of it represents the distance, which is to be compared with the scale there is disposed a nut Z To the latter is fixed by its one end a bridge g.

which rests by its other end by means of a ball 7 on the guide bar a. This bridge collective carries 'an o tical system which consists of a collective ens m and a rectangular, isosceles prism on, whose hypotenusal surface forms a reflecting surface, and which in conjunction with this si hting telescope m serves for sighting at he scale 1). The system m m whose optical axis runs in the plane determined by the common axis A--A of the points and y" and by the scale 1), is constructed and disposed in such a way that its focal point lies on the scale 79 and the front negative nodal point of the collective lehs m 1n the axis A-A. Of the points 9' and 7' of the gripping appliance the former, 9' is displaceable in the bearing pedestal k with the aid of a screw 8 in the axial direction, whilst the latter" j", which carries, on the one hand a stud s for thescrew bolt 2 and, on the other hand, a drum 8 fitted with a scale, is rotatable about its axis but not displaceable in the direction of this axis. Finally it may be mentioned that the telescope m is provided with a micrometer ocular m".

If it be desired to examine with this device the pitch of the screw bolt Z, it is necessary to rotate repeatedly the point 9' with the aid of the drum 8*, e. g. through 360 each, whereby the nut Z and consequently the bridge and the optical system m, m are dis laced in the direction of the bolt-axis A The amount of the displacement is then read ofi' on the scale, 11 with the aid of the micrometer ocular m.

I claim: I

In a device for comparing tw distances, running arallell to each other, a fixed sighting evice a apted to observe the one of these two distances, an optical system located in front of the said sighting device and displaceable parallelly to these distances, the optical axis of which system lies o'rro nrrnns'rnrn. 

